Back-up pads are used in the abrasives field to support an abrasive disc or sheet during abrading. The term “abrading” as used herein includes all methods of material removal due to frictional contact between contacting surfaces in relative motion, such as grinding, sanding, polishing, burnishing, or refining. The abrasive articles can be any suitable abrasive article such as coated abrasives, lapping coated abrasives, non-woven abrasives or buffing pads. These abrasive articles can be in various forms, such as a disc, a sheet, or a polygon and, may optionally, contain holes or slits to aid in dust extraction. The back-up pad includes a generally planar major surface, to which the abrasive article, such as a disc or sheet, may be attached. Although back-up pads may be hand held, back-up pads are more commonly used in conjunction with a powered abrading apparatus such as electric or pneumatic sanders.
Abrasive discs and sheets (hereinafter “discs”) may be attached to a back-up pad in various ways. One attachment method includes an abrasive disc having pressure sensitive adhesive (PSA) on one surface thereof, such that the abrasive disc may be adhered to the major surface of the back-up pad. The major surface of the back-up pad may have, for example, a smooth foam, vinyl, or cloth surface to facilitate attachment of the abrasive disc. An example of such a back-up pad is available from 3M Company of St. Paul, Minn., under the designation “STIKIT” brand back-up pad. An example of an abrasive disc for attachment to that back-up pad is available from the same company under the designation “STIKIT” brand abrasive disc.
A second type of back-up pad includes a major surface having a plurality of hooks projecting therefrom. The hooks are adapted to engage certain structures provided on the back face of an abrasive disc to releasably attach the disc to the back-up pad. An example of such a back-up pad is available from the 3M Company of St. Paul, Minn., under the designation “HOOKIT” brand back-up pad, and an example of an abrasive disc for attachment to that back-up pad is available from the same company under the designation “HOOKIT” brand abrasive disc. Alternatively, the back-up pad major surface can include engaging structures to cooperate with hooks on an abrasive disc. An example of such an assembly is available from 3M Company under the designation “HOOKIT II” brand back-up pad and abrasive disc.
The back-up pads described above are often used with dual action sanders (“DA sanders”), which are well known in the art. Such sanders with back-up pads may be used for light duty sanding operations such as light sanding of painted surfaces between paint coats and sanding with very fine sandpaper to remove small paint imperfections such as dust nibs from the final paint coat. This type of sanding imparts light stress to the attachment interface. Such back-up pads may also be used for medium duty sanding operations such as final preparation of a workpiece surface for primer painting and sanding a workpiece surface having a primer paint thereon in preparation for subsequent painting. Light to medium downward pressures are typically applied during these types of sanding applications and impart a moderate amount of stress on the attachment interface. However, such sanders and back-up pads are often used under heavy duty sanding operations such as paint stripping or removing excess body filler where the operator would apply fairly heavy downward pressure. The back-up pad is often inclined at a relatively steep angle with respect to the workpiece surface and may also be pushed into crevices and over fairly sharp contours. The paint or body filler on the workpiece surface provides substantial resistance to the abrasive surface of the abrasive article attached to the back-up pad so that a considerable sanding force is often required to remove the paint or body filler. Such aggressive, heavy sanding operations apply substantial stress on the hook and loop attachment interface.